1. Field of the Invention
The present invention relates to a polishing slurry for chemically mechanically polishing a surface of a GaxIn1−xAsyP1−y crystal used in a substrate for a semiconductor device such as a light emitting element, an electronic element and a semiconductor sensor, a method of treating a surface of a GaxIn1−xAsyP1−y crystal using the polishing slurry, and a GaxIn1−xAsyP1−y crystal substrate obtained by the surface treating method.
2. Description of the Background Art
A GaxIn1−xAsyP1−y crystal (0≦x≦1, 0≦y≦1) such as a GaAs crystal and an InP crystal is very useful as a material for forming a substrate of a semiconductor device such as a light emitting element, an electronic element and a semiconductor sensor.
The GaxIn1−xAsyP1−y crystal substrate (0≦x≦1, 0≦y≦1) used as a substrate for a semiconductor device is obtained by subjecting an external circumference of a GaxIn1−xAsyP1−y crystal to shape forming processing, slicing the crystal to have a predetermined thickness, and grinding or lapping a surface thereof and, by such the slicing and, grinding or lapping, a procession denatured layer (this refers to a layer in which crystal lattices are disturbed, which is formed on a surface side region of a crystal by processing a crystal surface; the same hereinafter) is formed on a surface side region of the GaxIn1−xAsyP1−y crystal, and a roughness of a surface of the GaxIn1−xAsyP1−y crystal becomes great.
As a thickness of the procession denatured layer of this GaxIn1−xAsyP1−y crystal substrate becomes greater, or as a surface roughness thereof becomes greater, quality of a substrate surface is deteriorated, irregularities of a surface of a Group III-V compound crystal layer which is epitaxial-grown on this GaxIn1−xAsyP1−y crystal become great, and crystallizability of the surface is deteriorated. For this reason, a semiconductor device of better quality cannot be formed.
For this reason, as a method of forming a GaxIn1−xAsyP1−y crystal substrate from a GaxIn1−xAsyP1−y crystal, the following method is widely performed: a GaxIn1−xAsyP1−y crystal is sliced to have a predetermined thickness, a surface thereof is ground or lapped and, further, the surface is polished chemically and mechanically, thereby, a procession denatured layer of a GaxIn1−xAsyP1−y crystal is removed, and a surface roughness is reduced.
As a polishing slurry for chemically mechanically polishing a surface of the GaxIn1−xAsyP1−y crystal, a polishing slurry containing spherical colloidal silica abrasive grains, an inorganic salt, and alkali metal chlorinated isocyanurate which is an oxidizing agent (e.g. see Japanese Patent Publication No. 3077665 (hereinafter, referred to as Patent Document 1)), and a polishing slurry containing spherical colloidal silica abrasive grains, a mineral acid and persulfate which is an oxidizing agent (e.g. see Japanese Patent Laying-Open No. 64-087147 (hereinafter, referred to as Patent Document 2)) are proposed. In chemical mechanical polishing (hereinafter, referred to as CMP) using these polishing slurries, a surface of a GaxIn1−xAsyP1−y crystal is oxidized with an oxidizing agent and a mineral acid to form an oxidized layer, and this oxidized layer is removed with colloidal silica abrasive grains.
However, in polishing slurries shown in Patent Document 1 and Patent Document 2, since spherical colloidal silica abrasive grains are used as abrasive grains, a rate of polishing a GaxIn1−xAsyP1−y crystal is low due to a low rate of removing the oxidized layer, and an efficiency of CMP is low. When a colloidal silica abrasive grain having a large particle diameter is used, a polishing rate can be enhanced, but a surface roughness is increased. In addition, also when an abrasive grain having a higher hardness than that of a colloidal silica abrasive grain, such as an Al2O3 abrasive grain is used, a polishing rate can be enhanced, but since a new procession denatured layer is formed due to this abrasive grain having a high hardness, better surface quality can not be obtained.